In order to maximize the capacity of various rotary electric machines as, for example, generators, it is desirable to provide liquid cooling for various components such as windings. For example, it is not uncommon to spray a liquid coolant such as oil on the end turns of stator windings.
In many instances, this does not pose a particular problem. However, in the case of high speed rotary machines, the liquid coolant may enter the air gap between the rotor and the stator. The resulting churning of the coolant produces sizable drag losses on the machine with the consequence that the losses caused by such drag minimize or even exceed the increase in capacity achieved by liquid cooling.
In order to solve this difficulty, the prior art has typically resorted to the use of one or more physical barriers that are interposed between the windings being cooled and the air gap for the purpose of preventing the liquid coolant from traveling to the air gap. In addition to complicating the construction of the rotary electric machine, such barriers may also have an effect on its efficiency in that their presence frequently tends to increase the length of the magnetic flux path thus reducing magnetic efficiency of the device to some extent.
The present invention is directed to overcoming one or more of the above problems.